google/go-cmp

Readability of cmp.Diff function

amirrmonfared opened this issue · 7 comments

amirrmonfared commented

I believe we can make the readability of the Diff function output very much by just adding (-want +got)

mrwormhole commented

for the love of god, please @dsnet @neild

I still don't understand why cmp.Diff takes x and y, I have seen dozens of mistakes of mixing want and got (at least x means want and y means got, could there be a renaming for those pls)

  • 👍1
dsnet commented

I don't think this is going to change. This was discussed in the early days of cmp deployment, and people could not agree whether got or want comes first. People were relatively evenly split between both. In the lack of a uniform consensus, we went with an approach that avoids choosing a path.

Feel free to create a package that simply wraps cmp.Diff and injects the headers as you see fit.

  • 👍1
dsnet commented

For the record, I was in support of (-got +want), but there were a number of notable people on the Go team who instead argued for (-want +got). There are valid arguments for both:

  • For (-got +want), the argument is that it matches the conventional ordering of "got" appearing before "want".
  • For (-want +got), the argument is that it displays a diff of how the expected value was changed into the current value (i.e., what changed relative to the expected value).

The Go style guide remains ambiguous about what direction to use. Although, it seems to suggest want, got, but also seems to permit got, want.

  • 👍2
neild commented

And also, while "got" and "want" make sense in tests, Diff output isn't necessarily used only in tests.

Perhaps there should be a test-specific diff API with named parameters:

diff := cmp.C{
  Want: want,
  Got:  got,
}.Diff(opts)
  • 👍2
mrwormhole commented

very tricky, looks like it is not settled;

dsnet commented

When it comes to cmp.Equal it doesn't matter since the cmp guarantees symmetric property of equality.

mrwormhole commented

I found cmp.Diff example in google styling guide, I think it can be enforced pretty well if not, should be suggested on README.md perhaps, I will also check out other testing libraries and come back with my findings for - + or + -

https://google.github.io/styleguide/go/best-practices#tests

but you are absolutely right equality shouldn't care about want and got, it takes 2 numbers and return bool

perhaps at the end of the day + - and - + doesn't matter at all, just like yaml or yml where you stick one and in that repo everyone uses that side (aka eventual consistency)